A Disk-Based Margin Indicator for Stability Assessment of Multiconverter Power Systems

The growing integration of power electronic converters into power systems presents challenges to conventional stability analysis approaches. This paper proposes a stability indicator based on disk margin theory to evaluate the degree of system stability. It inherently avoids the stability assessment limitations of classical methods, such as the Generalized Nyquist Criterion (GNC), particularly when coexisting grid-forming (GFM) and grid-following (GFL) converters result in open-loop right-half-plane (RHP) poles. Additionally, the proposed indicator offers a simple computation procedure that directly yields the apparatus impedance margin to reflect the system strength without complex mathematical transformations, while simultaneously accounting for both gain and phase conditions to provide a comprehensive assessment. Furthermore, by evaluating the individual margin of each apparatus, the method facilitates the identification of instability sources and facilitates targeted improvements in overall system robustness.